1. Field of the Invention
The present invention relates to fluorescent lamp ballast control circuits.
2. Background Art
The use of fluorescent lamps has become widespread. The typical fluorescent lamp is composed of a glass tube containing an inert gas and a small amount of mercury. Phosphor coats the inside of the glass tube, and each end of the glass tube includes an electrode. In operation, a ballast provides current to the electrodes. A traditional ballast is a special transformer that uses electromagnetic principles to generate operating and starting voltages for fluorescent lamps. An electronic ballast uses electronics to achieve the same result. In operation, electrons migrate across the length of the tube, and excite the mercury atoms which are in a gaseous state. The arc releases photons in the ultraviolet band. The photons excite the phosphors that coat the inside of the glass tube, and the phosphors emit visible light.
One type of electronic ballast employs a ballast control integrated circuit (IC) to drive the fluorescent lamp. A ballast controller and half-bridge driver in one IC are described in Data Sheet No. PD60194, “DIMMING BALLAST CONTROL IC.”